Flame detecting system

ABSTRACT

A sensitivity parameter storing portion stores, as known sensitivity parameters owned by a flame sensor, reference received light quantity, reference pulse width, probability of regular discharge, and probabilities of non-regular discharge in advance. The discharge probability is calculated based on the number of drive pulses applied to the flame sensor and the number of discharges determined to have occurred in the flame sensor having received the drive pulses. The calculated discharge probability and the known sensitivity parameters are used to calculate the received light quantity per unit time received by the flame sensor.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of and priority to JapanesePatent Application No. 2016-225893, filed on Nov. 21, 2016, the entirecontents of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a flame detecting system that detectsthe presence or absence of a flame.

BACKGROUND ART

There is a conventionally known electron tube used to detect thepresence or absence of a flame on the basis of ultraviolet rays emittedfrom a flame in a combustion furnace or the like. The electron tubeincludes a sealed container in which predetermined gas is filled in asealing manner, two electrode supporting pins that penetrate throughboth end portions of the sealed container, and two electrodes (a pair ofelectrodes) that are supported in parallel with each other by theelectrode supporting pins within the sealed container.

In the electron tube, when one electrode facing a flame is irradiatedwith ultraviolet rays in a state where a predetermined voltage isapplied across the electrodes through the electrode supporting pins,electrons are emitted from the one electrode due to the photoelectriceffect and excited in succession one after another to cause an electronavalanche between the one electrode and the other electrode. Therefore,it is possible to detect the presence or absence of a flame by measuringa change in impedance between the electrodes, a change in voltagebetween the electrodes, and a change in current flowing between theelectrodes. Various methods for detecting the presence or absence of aflame have been suggested.

Of these methods, for example, there is one proposed method in whichcurrent flowing between the electrodes is integrated and the presence ofa flame is determined when the integrated value is greater than or equalto a predetermined threshold value or the absence of a flame isdetermined when the integrated value is less than the predeterminedthreshold value (see, for example, PTL 1).

However, since this method integrates the current flowing between theelectrodes, the time for integration is required even in flameextinction. Accordingly, it takes time until flame extinction isdetected, consequently making it difficult to detect the presence orabsence of a flame rapidly.

In order to solve the problems described above, the flame detectingdevice disclosed in PTL 2 includes an electron tube in which a pair ofelectrodes are provided and electrons are emitted between the electrodeswhen the electrodes are irradiated with ultraviolet rays, an applyingportion that applies a periodically changing voltage across theelectrodes, a detecting portion that detects a voltage waveformrepresenting a temporal change of the voltage between the electrodes,and an determining portion that determines the presence or absence of aflame on the basis of the voltage waveform detected by the detectingportion.

Since the flame detecting device disclosed in PTL 2 determines thepresence or absence of a flame on the basis of the voltage waveformrepresenting the temporal change of the voltage between the electrodesprovided in the electron tube, the time for integration or the like isnot required and the presence or absence of a flame can be detectedrapidly.

CITATION LIST Patent Literature

[PTL 1] JP-A-2011-141290

[PTL 2] JP-A-2013-210284

SUMMARY

However, the flame detecting device disclosed in PTL 2 needs to monitorthe voltage waveform representing the temporal change of the voltagebetween the electrodes and to perform signal processing in an analogmanner in order to find the rise, fall, and the like on the basis of themonitored voltage waveform, so the implementation of the flame detectingdevice is not easy.

The invention addresses the above problems with an object of providing aflame detecting system capable of detecting the presence or absence of aflame accurately in a simple structure without the need for signalprocessing in an analog manner.

To achieve the above object, according to the invention, there isprovided a flame detecting system including a flame sensor (1)configured to have a pair of electrodes and detect light generated froma flame; an applied voltage generating portion (12) configured toperiodically generate a pulsed voltage and apply the voltage across thepair of electrodes of the flame sensor as drive pulses; a currentdetecting portion (15) configured to detect current flowing through theflame sensor; a storing portion (19) for storing, as known sensitivityparameters owned by the flame sensor, at least a reference receivedlight quantity Q₀ of the flame sensor, a reference pulse width T₀ of thedrive pulses applied across the pair of electrodes of the flame sensor,a probability P₀ of regular discharge generated between the pair ofelectrodes, and a probability P_(N) of discharge other than the regulardischarge, a quantity of received light of the flame sensor being thereference received light quantity Q₀, a pulse width of the drive pulsesapplied to the flame sensor being the reference pulse width T₀; anumber-of-discharges counting portion (201) configured to count thenumber n of discharges determined to have occurred across the pair ofelectrodes of the flame sensor based on the current detected by thecurrent detecting portion when the drive pulses generated by the appliedvoltage generating portion are applied across the pair of electrodes ofthe flame sensor; and a received light quantity calculating portion(203) configured to calculate a received light quantity Q per unit timereceived by the flame sensor based on the known sensitivity parametersstored in the storing portion, a pulse width T and a number N of thedrive pulses applied across the pair of electrodes of the flame sensorby the applied voltage generating portion, and the number n ofdischarges counted by the number-of-discharges counting portion when thedrive pulses are applied across the pair of electrodes of the flamesensor.

In the invention, the pulsed voltage is periodically applied to theflame sensor as drive pulses. In addition, the storing portion stores,as the known sensitivity parameters owned by the flame sensor, thereference received light quantity Q₀, the reference pulse width T₀, theprobability P₀ of regular discharge, and the probability P_(N) ofdischarge other than the regular discharge. The received light quantitycalculating portion calculates the received light quantity Q per unittime received by the flame sensor based on the known sensitivityparameters (reference received light quantity Q₀, reference pulse widthT₀, probability P₀ of regular discharge, and probability P_(N) ofdischarge other than the regular discharge) stored in the storingportion, the pulse width T and the number N of the drive pulses appliedacross the pair of electrodes of the flame sensor, and the number n ofdischarges counted when the drive pulses are applied across the pair ofelectrodes of the flame sensor.

In the invention, the pulse width T of the drive pulses applied to theflame sensor is known, the reference received light quantity Q₀, thereference pulse width T₀, the probability P₀ of regular discharge, andthe probability P_(N) of discharge other than the regular discharge arealso stored as known sensitivity parameters, and the pulse width T ofthe drive pulses applied across the pair of electrodes of the flamesensor is also known, so it is possible to calculate the received lightquantity Q per unit time received by the flame sensor based on thenumber N of the drive pulses applied to the flame sensor and the numbern of discharges determined to have occurred in the flame sensor havingreceived the drive pulses. The presence or absence of a flame can bedetected based on the calculated received light quantity Q. In addition,in the invention, the known sensitivity parameters used to calculate thereceived light quantity Q include the probability P_(N) of dischargeother than the regular discharge in addition to the probability P₀ ofregular discharge. With this, the presence or absence of a flame can bedetected accurately.

In the above description, the components in the drawings correspondingto components of the invention are indicated by reference numeralsenclosed in parentheses.

According to the invention, the presence or absence of a flame can bedetected accurately in a simple structure since the received lightquantity Q per unit time received by the flame sensor is calculatedbased on the reference received light quantity Q₀, the reference pulsewidth T₀, the probability P₀ of regular discharge, and the probabilityP_(N) of discharge other than regular discharge stored as the knownsensitivity parameters, the pulse width T and the number N of the drivepulses applied across the pair of electrodes of the flame sensor, andthe number n of discharges counted when the drive pulses are appliedacross the pair of electrodes of the flame sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the main part of a flame detecting system accordingto an embodiment of the invention.

FIG. 2 is a waveform diagram illustrating drive pulses PM applied to aflame sensor, a detected voltage Vpv detected in a current detectingcircuit, and the presence or absence of a flame in this flame detectingsystem.

FIG. 3 is a flowchart illustrating an operational process until thepresence or absence of a flame is detected in the flame detectingsystem.

DETAILED DESCRIPTION

Embodiments of the invention will be described in detail below withreference to the drawings. FIG. 1 illustrates the main part of a flamedetecting system 100 according to an embodiment of the invention. Theflame detecting system 100 includes a flame sensor 1, an external powersupply 2, and a calculating device 3 to which the flame sensor 1 and theexternal power supply 2 are connected.

Although not illustrated, the flame sensor 1 has an electron tubeincluding a cylindrical envelope whose both end portions are closed, twoelectrode pins that penetrate through both end portions of the envelope,and two electrodes (a pair of electrodes) that are supported in parallelwith each other by the electrode pins within the envelope.

In such an electron tube, one electrode is disposed so as to face adevice such as a burner which generates a flame 300. With this, when oneelectrode is irradiated with ultraviolet rays in a state where apredetermined voltage is applied across the electrodes, electrons areemitted from the electrode due to the photoelectric effect and excitedin succession one after another to cause an electron avalanche betweenone electrode and the other electrode. This changes the voltage,current, and impedance between the electrodes.

The external power supply 2 includes a commercial AC power supply havinga voltage value of, for example, 100 V or 200 V.

The calculating device 3 includes a power supply circuit 11 connected tothe external power supply 2, an applied voltage generating circuit 12and a trigger circuit 13 connected to the power supply circuit 11, avoltage dividing resistor 14 including resistors R1 and R2 connected inseries between a downstream side terminal 1 b of the flame sensor 1 anda ground line GND, a current detecting circuit 15 for detecting avoltage (reference voltage) Va generated at a connection point Pabetween the resistors R1 and R2 of the voltage dividing resistor 14 ascurrent I flowing through the flame sensor 1, and a processing circuit16 to which the applied voltage generating circuit 12, the triggercircuit 13, and the current detecting circuit 15 are connected.

The power supply circuit 11 supplies AC electric power input from theexternal power supply 2 to the applied voltage generating circuit 12 andthe trigger circuit 13. In addition, the electric power for driving thecalculating device 3 is obtained from the power supply circuit 11(however, the electric power for driving the calculating device 3 may beobtained from another power supply regardless of whether the electricpower is AC power or DC power).

The applied voltage generating circuit 12 boosts the AC voltage appliedby the power supply circuit 11 to a predetermined value and applies theAC voltage to the flame sensor 1. The embodiment generates a 200 Vpulsed voltage (voltage equal to or more than the discharge startingvoltage V_(ST) of the flame sensor 1) in sync with rectangular pulses PSfrom the processing circuit 16 as drive pulses PM and applies thegenerated drive pulses PM to the flame sensor 1. FIG. 2(a) illustratesthe drive pulses PM to be applied to the flame sensor 1. The drivepulses PM synchronize with the rectangular pulses PS from the processingcircuit 16 and the pulse width T thereof is equal to the pulse width ofthe rectangular pulses PS. The rectangular pulses PS from the processingcircuit 16 will be described later.

The trigger circuit 13 detects a predetermined value point of the ACvoltage applied by the power supply circuit 11 and inputs the detectedresult to the processing circuit 16. In the embodiment, the triggercircuit 13 detects the minimum value point at which the voltage value isminimized as a predetermined value point (triggering time point). Bydetecting a predetermined value point regarding an AC voltage in thismanner, it is possible to detect one cycle of the AC voltage.

The voltage dividing resistor 14 generates the reference voltage Va as adivided voltage by the resistors R1 and R2 and inputs the referencevoltage Va to the current detecting circuit 15. Since the voltage valueof the drive pulses PM applied to an upstream side terminal 1 a of theflame sensor 1 is a high voltage of 200 V as described above, if thevoltage generated at the terminal 1 b downstream of the flame sensor 1is input to the current detecting circuit 15 as is when current flowsbetween the electrodes of the flame sensor 1, a heavy load is applied tothe current detecting circuit 15. Accordingly, in the embodiment, thevoltage dividing resistor 14 generates the reference voltage Va having alow voltage value and inputs the reference voltage Va to the currentdetecting circuit 15.

The current detecting circuit 15 detects the reference voltage Va inputfrom the voltage dividing resistor 14 as current I flowing through theflame sensor 1 and inputs the detected reference voltage Va to theprocessing circuit 16 as a detected voltage Vpv.

The processing circuit 16 includes a rectangular pulse generatingportion 17, an A/D converting portion 18, a sensitivity parameterstoring portion 19, a central processing portion 20, and a determiningportion 21.

The rectangular pulse generating portion 17 generates the rectangularpulse PS having the pulse width T each time the trigger circuit 13detects a triggering time point (that is, every cycle of an AC voltageapplied from the power supply circuit 11 to the trigger circuit 13). Therectangular pulses PS generated by the rectangular pulse generatingportion 17 are sent to the applied voltage generating circuit 12.

The A/D converting portion 18 performs A/D conversion of the detectedvoltage Vpv from the current detecting circuit 15 and sends theconverted voltage to the central processing portion 20. The sensitivityparameter storing portion 19 stores, as the known sensitivity parametersowned by the flame sensor 1, a reference received light quantity Q₀, areference pulse width T₀, a regular discharge probability P₀,probabilities P_(N) (P_(N1), P_(N2), and P_(N3)) of discharge other thanregular discharge, which will be described later. The probability P_(N)of discharge other than regular discharge is called the probabilityP_(N) of non-regular discharge.

The central processing portion 20 is implemented by hardware including aprocessor and a memory device and a program for achieving variousfunctions in cooperation with such hardware, and the central processingportion 20 includes a discharge determining portion 201, a dischargeprobability calculating portion 202, and a received light quantitycalculating portion 203.

In the central processing portion 20, the discharge determining portion201 compares the detected voltage Vpv input from the A/D convertingportion 18 with a predetermined threshold voltage Vth (see FIG. 2(b))each time the drive pulse PM is applied to the flame sensor 1 (each timethe rectangular pulse PS is generated) and, when the detected voltageVpv exceeds the threshold voltage Vth, determines that the flame sensor1 has discharged.

The discharge probability calculating portion 202 obtains the number nof discharges determined to have occurred by the discharge determiningportion 201 each time the number of pulses of the drive pulses PMapplied to the flame sensor 1 reaches N (the number of pulses of therectangular pulses PS reaches N) and calculates the dischargeprobability P (P=n/N) of the flame sensor 1 based on the obtained numbern of discharges and the number N of pulses of the drive pulses PMapplied to the flame sensor 1.

The received light quantity calculating portion 203 calculates thereceived light quantity Q per unit time received by the flame sensor 1using Equation 8, which will be described later, based on the knownsensitivity parameters (the reference received light quantity Q₀, thereference pulse width T₀, the probability P₀ of regular discharge, andthe probabilities P_(N) (P_(N1), P_(N2), and P_(N3)) of non-regulardischarge) stored in the sensitivity parameter storing portion 19, thepulse width T (pulse width T of the rectangular pulses PS) of the drivepulse PM applied to the flame sensor 1, the probability P (P=n/N) ofdischarge computed by the discharge probability calculating portion 202.

It should be noted that the calculation of the received light quantity Qwith Equation 8 is performed when the discharge probability P is 0<P<1.When the discharge probability P is 0, the received light quantity Q is0. When the discharge probability P is 1, such processing does notapply.

The received light quantity Q calculated by received light quantitycalculating portion 203 is sent to the determining portion 21. Thedetermining portion 21 compares the received light quantity Q from thereceived light quantity calculating portion 203 with a predeterminedthreshold Qth and, when the received light quantity Q exceeds thethreshold Qth, determines that a flame is present.

About Sensitivity Parameter

It is assumed that the probability that discharge occurs when a singlephoton collides with the flame sensor 1 is P₁ and the probability thatdischarge occurs when two photons collide with the flame sensor 1 is P₂.Since P₂ is obtained by subtracting, from 1, the probability thatdischarge does not occur when the first photon collides with thephotoelectric sensor and the second photon collides with thephotoelectric sensor, the relationship between P₁ and P₂ is expressed asEquation 1 below.

[Equation 1]

(1−P ₂)=(1−P ₁)²  (1)

In general, when it is assumed that the probability that dischargeoccurs when n photons collide is P_(n) and the probability thatdischarge occurs when m photons collide is P_(m), Equation 2 andEquation 3 are established similarly to Equation 1.

[Equation 2]

(1−P _(n))=(1−P ₁)^(n)  (2)

[Equation 3]

(1−P _(m))=(1−P ₁)^(m)  (3)

The following Equations 4 and 5 representing the relationship betweenP_(n) and P_(m) are drawn based on Equations 2 and 3.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack & \; \\{\left( {1 - P_{n}} \right)^{\frac{1}{n}} = \left( {1 - P_{m}} \right)^{\frac{1}{m}}} & (4) \\\left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack & \; \\{\left( {1 - P_{n}} \right) = \left( {1 - P_{m}} \right)^{\frac{n}{m}}} & (5)\end{matrix}$

The number of photons contributing to discharge is determined by theproduct of the number Q of photons (received light quantity per unittime) that reach the electrodes of the flame sensor 1 per unit time andtime T (pulse width T) for which a voltage equal to or more than thedischarge starting voltage V_(ST) is applied to the flame sensor 1. Whenthe reference received light quantity Q₀ and the reference pulse widthT₀ are determined and the discharge probability at this time is definedas P₀, the received light quantity Q, the pulse width T, and thedischarge probability P at that time are represented by Equation 6below.

[Equation  6] $\begin{matrix}{\left( {1 - P} \right) = \left( {1 - P_{0}} \right)^{\frac{QT}{Q_{0}T_{0}}}} & (6)\end{matrix}$

However, the flame sensor 1 causes the following three types ofnon-regular discharge when the discharge (discharge that occurs betweena pair of electrodes when the received light quantity of the flamesensor 1 is the reference received light quantity Q₀ and the pulse widthof drive pulses to be applied to the flame sensor 1 is the referencepulse width T₀) that occurs at the discharge probability P₀ is regulardischarge. It should be noted that non-regular discharge means dischargeother than regular discharge.

(1) Noise discharge N1 (first type non-regular discharge) that occurs ata constant probability per unit time within the pulse width T of thedrive pulses PM and occurs regardless of the number of photons receivedby the flame sensor 1.

(2) Noise discharge N2 (second type non-regular discharge) that occursat a constant probability for each of the drive pulses PM1 regardless ofthe pulse width T of the drive pulses PM and occurs depending on thenumber of photons received by the flame sensor 1.

(3) Noise discharge N3 (third type non-regular discharge) that occurs ata constant probability for each of the drive pulses PM regardless of thepulse width T of the drive pulses PM and occurs regardless of the numberof photons received by the flame sensor 1.

The probabilities P_(N) of occurrence of these three types of noisedischarge are defined as described below.

(1) The probability at which noise discharge N1 occurs per unit time isthe probability P_(N1) of the first type non-regular discharge.

(2) The probability at which noise discharge N2 occurs for one drivepulse PM1 when the number of photons is Q is the probability P_(N2) ofthe second type non-regular discharge.

(3) The probability at which noise discharge N3 occurs for one drivepulse PM1 is the probability P_(N3) of the third type non-regulardischarge.

At this time, Equation 6 in which P₀ is assumed to be the probability ofregular discharge is corrected as indicated in Equation 7.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack & \; \\{\left( {1 - P} \right) = {\left( {1 - P_{0}} \right)^{\frac{QT}{Q_{0}T_{0}}} \cdot \left( {1 - P_{N\; 1}} \right)^{\frac{T}{T_{0}}} \cdot \left( {1 - P_{N\; 2}} \right)^{\frac{Q}{Q_{0}}} \cdot \left( {1 - P_{N\; 3}} \right)}} & (7)\end{matrix}$

Base on Equation 7, the received light quantity Q per unit time receivedby the flame sensor 1 can be calculated using Equation 8 below.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack & \; \\{Q = {\log_{({{({1 - P_{0}})}^{\frac{T}{Q_{0}T_{0}}} \cdot {({1 - P_{N\; 2}})}^{\frac{1}{Q_{0}}}})}\left( \frac{1 - P}{\left( {1 - P_{N\; 1}} \right)^{\frac{T}{T_{0}}} \cdot \left( {1 - P_{N\; 3}} \right)} \right)}} & (8)\end{matrix}$

In Equation 8, since the pulse width T is the pulse width (pulse widthof the rectangular pulses PS) of the drive pulses PM applied to theflame sensor 1 and known, if the reference received light quantity Q₀,the reference pulse width T₀, the probability P₀ of regular discharge,the probabilities P_(N1), P_(N2), and P_(N3) of non-regular dischargeare known, unknown numbers are only the received light quantity Q andthe discharge probability P that are being measured.

Accordingly, in the embodiment the received light quantity Q per unittime received by the flame sensor 1 is calculated by applying the Ndrive pulses PM to the flame sensor 1, making a decision as to whetherthe flame sensor 1 has discharged for each of the N drive pulses PM,calculating the discharge probability P as P=n/N based on the number Nof pulses of the drive pulses PM having been applied to the flame sensor1 and the number n of times (number of discharges determined to haveoccurred) the flame sensor 1 has discharged by receiving the drivepulses PM, and substituting the calculated discharge probability P, theknown reference received light quantity Q₀, the known reference pulsewidth T₀, the known probability P₀ of regular discharge, the knownprobabilities P_(N1), P_(N2), and P_(N3) of non-regular discharge, andthe pulse width T into Equation 8.

The reference received light quantity Q₀, the reference pulse width T₀,the probability P₀ of regular discharge, the probabilities P_(N1),P_(N2), and P_(N3) of non-regular discharge need to be measured by, forexample, delivery inspection. Then, the reference received lightquantity Q₀, the reference pulse width T₀, the probability P₀ of regulardischarge, the probabilities P_(N1), P_(N2), and P_(N3) of non-regulardischarge that have been measured are stored in the sensitivityparameter storing portion 19 in advance as the known sensitivityparameters of the flame sensor 1.

Detection of the Presence or Absence of a Flame

An operational process until the presence or absence of a flame isdetected in the flame detecting system 100 will be described withreference to the flowchart illustrated in FIG. 3.

When the trigger circuit 13 detects a triggering time point, therectangular pulse generating portion 17 generates the rectangular pulsePS and sends the generated rectangular pulse PS to the applied voltagegenerating circuit 12. With this, the applied voltage generating circuit12 generates the drive pulse PM having the same pulse width T as therectangular pulse PS and the generated drive pulse PM having the pulsewidth T is applied to the flame sensor 1 (step S101).

When the drive pulse PM (voltage equal to or more than the dischargestarting voltage V_(ST)) has been applied to the flame sensor 1 and thecurrent I has flowed between the electrodes of the flame sensor 1, thecurrent I having flowed between the electrodes of the flame sensor 1 isdetected by the current detecting circuit 15 as the detected voltage Vpvand sent to the discharge determining portion 201 via the A/D convertingportion 18.

The discharge determining portion 201 compares the detected voltage Vpvfrom the current detecting circuit 15 with the predetermined thresholdvoltage Vth and, when the detected voltage Vpv exceeds the thresholdvoltage Vth, determines that the flame sensor 1 has discharged. Whendetermining that the flame sensor 1 has discharged, the dischargedetermining portion 201 counts the number n of discharges by 1 (stepS102).

Application of the drive pulses PM to the flame sensor 1 in step S101and counting of the number n of discharges in the flame sensor 1 in stepS102 are repeated until the number of applications of the drive pulsesPM to the flame sensor 1 reaches the predetermined number N times.

Then, when the number of applications to the flame sensor 1 reaches N(YES in step S103), the discharge probability calculating portion 202obtains the number n of discharges counted by the discharge determiningportion 201 and calculates the discharge probability P (P=n/N) of theflame sensor 1 based on the obtained number n of discharges and thenumber N of applications of the drive pulses PM to the flame sensor 1(step S104).

The discharge probability P calculated by the discharge probabilitycalculating portion 202 is sent to the received light quantitycalculating portion 203. The received light quantity calculating portion203 determines whether the discharge probability P meets 0<P<1 and, whenthe discharge probability P meets 0<P<1 (YES in step S105), calculatesthe received light quantity Q using Equation 8 above (step S106).

That is, the received light quantity Q per unit time received by theflame sensor 1 is calculated based on the known sensitivity parameters(the reference received light quantity Q₀, the reference pulse width T₀,the probability P₀ of regular discharge, and the probabilities P_(N)(P_(N1), P_(N2), and P_(N3)) of non-regular discharge) stored in thesensitivity parameter storing portion 19, the pulse width T of the drivepulses PM applied to the flame sensor 1, and the probability P (P=n/N)of discharge computed by the discharge probability calculating portion202.

In contrast, when the discharge probability P does not meet 0<P<1 (NO instep S105), that is, when the discharge probability P is 0 or 1, thereceived light quantity calculating portion 203 performs the exceptionprocessing of received light quantity (step S107). In the exceptionprocessing of received light quantity, the received light quantity Q isset to 0 when the discharge probability P is 0 or such processing doesnot apply when the discharge probability P is 1.

The received light quantity Q calculated by the received light quantitycalculating portion 203 is sent to the determining portion 21. Thedetermining portion 21 compares the received light quantity Q from thereceived light quantity calculating portion 203 with a predeterminedthreshold Qth and, when the received light quantity Q exceeds thethreshold Qth (YES in step S108), determines that a flame is present(step S109). When the received light quantity Q does not exceed thethreshold Qth (NO in step S108), the determining portion 21 determinesthat a flame is not present (step S110).

As is apparent from the above description, the flame detecting system100 according to the embodiment can calculate the received lightquantity Q per unit time received by the flame sensor 1 only bycalculating the discharge probability P (P=n/N) based on the number N ofpulses of the drive pulses PM applied to the flame sensor 1 and thenumber n of discharges during that time.

The presence or absence of a flame can be detected based on thecalculated received light quantity Q. In addition, the known sensitivityparameters used to calculate the received light quantity Q include theprobabilities P_(N) (P_(N1), P_(N2), and P_(N3)) of non-regulardischarge in addition to the probability P₀ of regular discharge. Withthis, the presence or absence of a flame can be detected accurately.

Although the probability P_(N1) of the first type non-regular discharge,the probability P_(N2) of the second type non-regular discharge, and theprobability P_(N3) of the third type non-regular discharge are used asthe probabilities P_(N) of non-regular discharge in the aboveembodiment, all of the probabilities P_(N1), P_(N2), and P_(N3) ofnon-regular discharge are not necessarily used. That is, any one of themmay be used or a combination of any two of them may be used.

For example, when only the probability P_(N1) of the first typenon-regular discharge is used, the probability P_(N2) of the second typenon-regular discharge and the probability P_(N3) of the third typenon-regular discharge only need to be set to 0 in Equation 8. Inaddition, when only the probability P_(N2) of the second typenon-regular discharge is used, the probability P_(N1) of the first typenon-regular discharge and the probability P_(N3) of the third typenon-regular discharge only need to be set to 0 in Equation 8. Inaddition, when only the probability P_(N3) of the third type non-regulardischarge is used, the probability P_(N1) of the first type non-regulardischarge and the probability P_(N2) of the second type non-regulardischarge only need to be set to 0 in Equation 8.

In addition, the probabilities P_(N) of non-regular discharge are notlimited to the probabilities of P_(N1), P_(N2), and P_(N3) ofnon-regular discharge (noise discharge N1, N2, and N3) defined asdescribed above in the invention.

In addition, although the drive pulses PM generated by the appliedvoltage generating circuit 12 are replaced with the rectangular pulsesPS generated by the rectangular pulse generating portion 17 and thenumber N of pulses and the pulse width T of the rectangular pulses PSare used as the number N of pulses and the pulse width T of the drivepulses PM in the above embodiment, the number N of pulses and the pulsewidth T of the actual drive pulses PM generated by the applied voltagegenerating circuit 12 may be used.

Expansion of Embodiment

Although the invention has been described with reference to the aboveembodiments, the invention is not limited to the above embodiments.Various changes understandable to those skilled in the art can be madeto the structure and details of the invention within the technicalspirit of the invention.

For example, shutter functionality can be provided on the envelope ofthe flame sensor for use in a flame detecting system for detecting apseudo flame. Although deformation is made in a matter of design, thedeformation is also included in the scope of the invention.

For example, although the external power supply 2 is an AC commercialpower source as illustrated in FIG. 1 in the above embodiment, a DCpower source may be used instead. In this case, the power supply circuit11 applies a DC voltage having a predetermined voltage value to theapplied voltage generating circuit 12 and the trigger circuit 13, thetrigger circuit 13 applies a DC voltage having a predeterminedrectangular waveform to the rectangular pulse generating portion 17 byturning on and off the applied DC current at predetermined cycles, andthe rectangular pulse generating portion 17 may be configured so as togenerate the rectangular pulses PS from the DC voltage having arectangular waveform and output the generated rectangular pulses PS.

In addition, the concept of an effective electrode surface area may beintroduced to the flame sensor. Then, it is possible to calculate thebrightness of the flame by dividing the received light quantity by theeffective electrode surface area. The effective electrode surface areameans the area on which light impinges of the electrode surface area ofthe flame sensor and the effective electrode surface area is a parameterunique to the flame sensor.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

1: flame sensor, 2: external power supply, 3: calculating device, 11:power supply circuit, 12: applied voltage generating circuit, 13:trigger circuit, 14: voltage dividing resistor, 15: current detectingcircuit, 16: processing circuit, 17: rectangular pulse generatingportion, 18: A/D converting portion, 19: sensitivity parameter storingportion, 20: central processing portion, 21: determining portion, 100:flame detecting system, 201: discharge determining portion, 202:discharge probability calculating portion, 203: received light quantitycalculating portion, 300: flame

1. A flame detecting system comprising: a flame sensor configured tohave a pair of electrodes and detect light generated from a flame; anapplied voltage generating device configured to periodically generate apulsed voltage and apply the pulsed voltage across the pair ofelectrodes of the flame sensor as drive pulses; a current detectingdevice configured to detect current flowing through the flame sensor; astorage device for storing, as known sensitivity parameters owned by theflame sensor, at least a reference received light quantity Q₀ of theflame sensor, a reference pulse width T₀ of the drive pulses appliedacross the pair of electrodes of the flame sensor, a probability P₀ of aregular discharge generated between the pair of electrodes, and aprobability P_(N) of a discharge other than the regular discharge, areceived light quantity of the flame sensor being the reference receivedlight quantity Q₀, a pulse width of the drive pulses applied to theflame sensor being the reference pulse width T₀; a number-of-dischargescounting portion configured to count a number n of discharges determinedto have occurred across the pair of electrodes of the flame sensor basedon the current detected by the current detecting device when the drivepulses generated by the applied voltage generating device are appliedacross the pair of electrodes of the flame sensor; and a received lightquantity calculating portion configured to calculate a received lightquantity Q per unit time received by the flame sensor based on the knownsensitivity parameters stored in the storage device, a pulse width T anda number N of pulses of the drive pulses applied across the pair ofelectrodes of the flame sensor by the applied voltage generating device,and the number n of discharges counted by the number-of-dischargescounting portion when the drive pulses are applied across the pair ofelectrodes of the flame sensor.
 2. The flame detecting system accordingto claim 1, wherein the probability P_(N) of a discharge other than theregular discharge includes a probability P_(N1) of a first typenon-regular discharge that occurs at a constant probability per unittime within the pulse width of the drive pulses and occurs regardless ofa number of photons received by the flame sensor.
 3. The flame detectingsystem according to claim 1, wherein the probability P_(N) of adischarge other than the regular discharge includes a probability P_(N2)of a second type non-regular discharge that occurs at a constantprobability for each of the drive pulses regardless of the pulse widthof the drive pulses and occurs depending on a number of photons receivedby the flame sensor.
 4. The flame detecting system according to claim 1,wherein the probability P_(N) of a discharge other than the regulardischarge includes a probability P_(N3) of a third type non-regulardischarge that occurs at a constant probability for each of the drivepulses regardless of the pulse width of the drive pulses and occursregardless of a number of photons received by the flame sensor.
 5. Theflame detecting system according to claim 1, wherein the probabilityP_(N) of a discharge other than the regular discharge includes aprobability P_(N1) of a first type non-regular discharge that occurs ata constant probability per unit time within the pulse width of the drivepulses and occurs regardless of a number of photons received by theflame sensor, a probability P_(N2) of a second type non-regulardischarge that occurs at a constant probability for each of the drivepulses regardless of the pulse width of the drive pulses and occursdepending on the number of photons received by the flame sensor, and aprobability P_(N3) of a third type non-regular discharge that occurs ata constant probability for each of the drive pulses regardless of thepulse width of the drive pulses and occurs regardless of the number ofphotons received by the flame sensor.
 6. The flame detecting systemaccording to claim 5, wherein the received light quantity calculatingportion is configured to calculate the received light quantity Q perunit time based on: $\begin{matrix}{Q = {\log_{\lbrack{{({1 - P_{0}})}^{\frac{T}{Q_{0}T_{0}}} \cdot {({1 - P_{N\; 2}})}^{\frac{1}{Q_{0}}}}\rbrack}\left\lbrack \frac{1 - P}{\left( {1 - P_{N\; 1}} \right)^{\frac{T}{T_{0}}} \cdot \left( {1 - P_{N\; 3}} \right)} \right\rbrack}} & (1)\end{matrix}$ wherein a discharge probability P is obtained based on thenumber N of pulses of the drive pulses applied to the flame sensor andthe number n of discharges determined to have occurred in the flamesensor having received the drive pulses.